CRT improves the exercise capacity and functional reserve of the failing heart through enhancing the cardiac flow- and pressure-generating capacity

Background: While information on how cardiac resynchronisation therapy (CRT) affects cardiac performance at rest is readily available, the mechanisms whereby CRT alters cardiac function during maximal exercise are unclear. Aims: We examined the medium-term effects of CRT on cardiac and physical functional reserve of patients with severe heart failure (CHF) and prolonged QRS duration. Methods: Seventeen consecutive patients with severe CHF (NYHA III–IV) and widened QRS underwent maximal cardiopulmonary exercise testing with non-invasive central haemodynamic measurements before and 6–8 weeks after CRT pacemaker implantation. Results After CRT there were significant increases in exercise cardiac output by 19.3% (P=0.0048) from 9.5±3.4 l min−1, peak mean arterial blood pressure by 14.1% (P=0.0001) from 91.3±13.6 mm Hg, and peak cardiac power output by 37.2% (P=0.0008) from 1.92±0.74 W. There were no significant changes in these variables at rest. Exercise duration (+42.3%, P=0.0002), NYHA functional class (P=0.0001) and SF-36 symptom score (P=0.0006) were also significantly improved. Powerful surrogate indicators of prognosis were also significantly improved with CRT: peak O2 consumption (+20.9%, P=0.0007), VE/VCO2 slope (−20.0%, P=0.005) and circulatory power (+42.0%, P=0.0012). Conclusion: In this cohort of patients, post-implant CRT significantly improved the flow-, pressure- and power-generating capacity of the failing hearts. This may be causally related to the improvements observed in exercise capacity, functional class and symptom scores.